Seasonal occurrence and microhabitat of the hyperparasitic monogenean Udonella fugu on the caligid Copepod Pseudocaligus fugu infecting the grass puffer Takifugu niphobles in the Seto Inland Sea, Japan

The seasonal occurrence and microhabitat of the monogenean Udonella fugu that hyperparasitizes exclusively on adults of the caligid copepod Pseudocaligus fugu that infects the skin of the grass puffer Takifugu niphobles were investigated in the Seto Inland Sea, western Japan from November 2004 to December 2006. The udonellids occurred and bred mostly during the occurrence of P. fugu on the fish host. The average prevalence and intensity of U. fugu on P. fugu during the whole investigation were 29% and 3.6, respectively. The main attachment sites of U. fugu were the posterior side of leg 3 and the dorsal marginal side of the cephalothorax for feeding and copulation, while eggs were predominantly located on the ventral side of the urosome to avoid detachment. More attention should be paid to the ecology of U. fugu, due to recent high prevalence of P. fugu on cultured tiger puffer in western Japan.